Unsolved Problems in Number Theory

To many laymen, mathematicians appear to be problem solvers, people who do "hard sums". Even inside the profession we dassify ourselves as either theorists or problem solvers. Mathematics is kept alive, much more than by the activities of either dass, by the appearance of a succession of unsolved problems, both from within mathematics-itself and from the in­ creasing number of disciplines where it is applied. Mathematics often owes more to those who ask questions than to those who answer them. T